MICROSTRUCTURE AND MAGNETIC PROPERTIES OF Sm_2Co+(17)-BASED HIGH TEMPERATURE PERMANENT MAGNETS

High temperature SniaCo17-based permanent magnets have been attained and the microstructures have been investigated by TEM, MFM and high-temperature XRD. The coercivity of the magnets at high temperature gradually increases with increasing Cu content, but decreases with Fe content increasing. The magnet has a cellular structure consisting of 2 : 17R phase in cell interior and 1 : 5 phase at cell boundary. Lamellar phase (1:7 phase), wavy domain wall and strip domain wall can be found by MFM. But no distinctive domain wall pinning sites along the lamellar phase were observed. At the triple junction of cell boundaries, the domain wall pinning strength is the highest. XRD shows that 2 : 17.R, 1 : 5 and 1 : 7 phases are transformed into amorphous phase at 500 ℃, and ultimately SmCo3 and 2 : 17R formed at 700 ℃, accompanied by a degradation of magnetic properties of the magnets.